JP2006050636A - Central coordinator selection method in ad hoc network - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for selecting a central coordinator in an ad hoc network. <P>SOLUTION: The method is disclosed herein, employable in the task, during organizing of the ad hoc network from a collection of plural nodes, of selecting a central coordinator node, where such organizing is taking place in a setting wherein there is available, to all of the nodes in the collection, a topology map describing, for all of the nodes, their respective identities, capabilities, and associated inter-nodal communication link numbers and qualities. The method includes the steps of (a) engaging all of the nodes in activity leading to an analysis of the topology map, and (b) from such engaging, and from the resulting nodal analysis, implementing an all-nodal participatory process to establish at least a predesignation of best candidate(s) to become the thereafter selected central coordinator node. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to self-organization of an ad hoc multi-node communication network, and more particularly to selecting a central coordinator node (CCo) in such a network. This selection is preferably implemented in certain different ways, as will be understood later, but all such aspects are effectively referred to herein as related to full node participation. This specification describes two specific implementations of the invention, one relating to a distributed network and the other relating to a centralized network.

  In implementing the present invention, certain predecessor organizing activities have already been undertaken, and in particular, these activities are formed so that a complete topology map of the appearing target network can be used for organizing. Is considered to be. These “previous activities” are the nature of ongoing “background” network organization activities associated with the dynamic creation and re-creation of time-consuming maps, if desired. obtain. In such a dynamic situation, the “previous” status from which the present invention starts is whatever is the current status of the “dynamic” topology map. Thus, reference herein to selecting a central coordinator node is intended to include the concept of combining such selection activities into a dynamic topology map configuration process in the configuration of an appropriate network. . When such a combination actually occurs, the central coordinator selection process itself becomes an existing, dynamic and transitional implementation, which means that the “currently selectable” best CCo is always so-called everywhere. Provides significant flexibility and ability to guarantee.

  Such a topology map identifies all participating nodes and describes each corresponding attribute, capability and condition (quality) of selectivity between nodes. From such map information, network organization chooses the best candidate nodes to CCo, identifies so-called hidden and proxy nodes, and best reproducible and most efficient of high-quality bi-directional communication links between nodes Can proceed in a good manner to achieve an organized network that provides a typical pattern.

  Briefly describing certain terminology used herein, a hidden node (HN) is a node that cannot "see" the selected CCo or that the selected CCo cannot "see" A proxy node (PCo) is a node that acts as a proxy CCo in an indirect communication path between a hidden node and a selected CCo, and the proxy node is a hidden node Facilitate communication between.

  The selection of CCo can be done in a number of different situations, for example (a) during the initial (initial) network organization, (b) under various dynamic and / or changing conditions, for example (1) When leaving the network, or when a new node enters the network, (2) when a network incident occurs that requires organizational recovery, and (3) the current CCo is no longer for its role This is advantageous when, for example, the best candidate node is not visible.

  The CCo selection process proposed by the present invention is very similar in various ways in the case of different networks including (a) distributed networks and (b) centralized networks. There are specific differences that result from two different assumptions that are each associated with two different types of networks. In an organization process involving a distributed network, the basic assumption is that there is not yet a selected CCo, and the opposite assumption is true for a process involving a centralized network.

  In an organized process involving a distributed network, all nodes participate in the CCo decision (selection) by performing an individual analysis on a “copy” of the complete network topology map owned by each node. From these analyses, and by applying the predetermined rules and priorities described herein, all nodes make choices regarding what they consider as the best selectable CCo. The join condition between competing candidate nodes for that role is resolved in the manner described in the detailed description of the present invention.

  In an organizational process involving a centralized network, the above assumptions relating to this type of network effectively cause the very first node (single device) to enter the network and self-declare itself as CCo. . This declaration examines the individually discovered node list owned by all of the participating nodes, and therefore, based on selecting the best candidate CCo, an appropriate analysis of the complete network topology map performed by that node. Only after it has been made will it be positively confirmed, even if it was made.

  Valid and relevant background information, which is incorporated herein by reference, is the continuation of the earlier application filed by the applicant on February 9, 2004, in an ad hoc network with a central controller. US patent application Ser. No. 10 / 775,717 and “Distributed Network Organization and Topology Discovery in Ad Hoc Networks”, whose title is “Centralized Network Organization and Topology Discovery” In US patent application Ser. No. 10 / 775,967.

  Various advantages and features of the present invention will become more apparent with respect to the selection of a central coordinator node in an ad hoc network of the type described above by reading the following detailed description with reference to the accompanying drawings.

  First, refer to FIG. Shown here are five nodes 20, 22, 24, 26, 28, each marked with an alphabet A, B, C, D, E, which are illustrative of two possible networks: Organized into network topologies 30 and 32. These topologies 30, 32 are also referred to herein as Net1 and Net2, respectively. The effective interconnections associated with the organization for these two explanations are 34 (between A and B), 36 (between A and C), 38 (between B and C). , 40 (between C and D), 42 (between C and E), and 44 (between D and E).

  Considering these two topologies, i.e., two configurations, first considering that any of the nodes can be CCo, Net1 (30) has Node A as CCo and Nodes B and C as hosts in the network. As can be seen, having node C as a PCo for hidden nodes D and E. Net2 (32) has node C as CCo, nodes D and E as hosts in the network, and node C as PCo for hidden nodes A and B. In a network with only nodes A, B and C as host nodes and node A as CCo, nodes D and E remain unconnected. When the quality (capacity) of the link between the CCo and another node changes, based on the traffic load handled by the node selected as the CCo among several other factors (separate from the CCo) ) Due to the overhead of having a node function as a PCo, the network performance is significantly different between the two configurations. In Net2, node C can operate as both CCo and PCo and can communicate with all four other nodes. In Net1, node A as CCo can only communicate directly with the other two nodes (B and C) and requires a proxy to handle nodes D and E.

  Reference is now made to the node placement described in FIG. 1, which illustrates the CCo selection process of the present invention.

  In a suitable way that does not form part of the present invention, a method to be referred to herein as a topology discovery method, ie a set of nodes, eg a set of nodes, eg a set of nodes as shown in FIG. Implement topologies and create complete and useful topology maps or tables in one form or another. Such a map fully describes the identities of all nodes that are willing to participate, as well as related characteristics that must be known to organize an effective network, including node characteristics and capabilities, and especially within node pairs. Describes the state of connectivity between nodes that exist between nodes. FIG. 3 shows a portion of such an overall topology map, including information about the so-called discovered node list of each participating node. In particular, FIG. 3 shows the entire individual topology table owned by nodes A and D in FIG.

  With respect to such a topology map, the following assumptions are made. In the case of a distributed network, a copy of this map depends on what each node in the network being organized owns. In a centralized network, the entire topology table or map basically depends on what node is currently operating as the CCo (how to determine the initial CCo for such a network). See previous explanation for what can be put in place).

  In particular, explaining what is shown in FIG. 3, and further this explanation for node A, the topology table for this node will have its own discovered node list (A, B, C). Since node A should also be considered the current CCo in this figure, this node in the centralized network maintains the discovered node lists of nodes D and E as well. In this example, these nodes D and E are hidden nodes. In a distributed network all nodes have this same knowledge.

  The rows in FIG. 3 correspond to the discovered node list received from a given node (an individually locally owned node list that provides a locally owned topology map for each node). For example, the discovered node list of node A is (A, B, C), the discovered node list of node C is (A, B, C, D, E), and the discovered node list of node D The list is (C, D, E) and so on.

  FIG. 3 is created to show that node B can listen to node C, but node C may not be able to listen to node B. This means that the link between Nodes B and C does not work in both directions (ie not bidirectional) and therefore is not a valid link. This state is indicated by (X) in the discovered node list from node B in node A's topology table. Node B is shown in the list of node C.

  If you are familiar with the corresponding technology regarding the topology of the network, you will find the contents of FIG. 3 self-evident. From the information contained in the entire network topology table as partially shown in FIG. 3, the process of CCo selection proceeds.

  For both types of network organizations described herein, what follows immediately after the discovery and construction of a complete topology table includes several steps or stages preceding the final selection of CCo. . Some of these predecessors are described under the three headings that follow this specification.

Analysis of topology table Here, the analysis process of the topology table is examined. Let D _A denote the discovered node list for node A, ie the set consisting of the identities of all nodes that node A has heard.

Next, as a table of the discovered nodes lists for all the nodes in D _A, define the topology table for node A. That is, it is shown as follows.

Non-bidirectional link detection Consider two nodes i and j. If node i is discovered by node j, i.e. the identity of i is an entry in node j's discovered node list, and node j is not discovered by node i, i.e. i If there is no entry for node j in the discovered node list, the link between i and j is said to be non-bidirectional.

  For any two nodes i and k

  i and k have bidirectional links i <=> k.

Network Organization A network can be defined as the largest set of nodes from a group of nodes that participate in the topology discovery and network organization process, where any node in the set and any other node listens. And can be listened to by any node in the set. This means that all nodes in the network have bi-directional links with each other.
Define as follows.

  The second condition present in the above equation is optional. Thus, a network can simply be defined as any set of nodes in which nodes are connected bi-directionally. The node can determine the network N based on the above definition by examining the topology table and judging the set of nodes having the characteristics defined in this equation.

  Turning now to FIG. 2, there are seven solid blocks 46, 48, 50, 52, 54, 56, 58 and one chain block 60, which are distributed. The method of implementing the present invention is shown generally in a slightly different manner for two different types of ad hoc networks, and the present invention will now be described in connection with these distributed and centralized networks. Considering FIG. 2 in a general way of visualizing how the present invention is implemented, block 46 shows the entire topology table as shown in part in FIG. If such a map is available, all nodes in the emerging network are involved in the analysis of the map (block 48), apply predetermined selection / designation criteria (block 50), and as described immediately below, Preliminarily designate what seems to be the best candidate for network CCo (block 52). Some of the activities associated with blocks 46-52 have been described in detail in three parts under the headings "Analysis of topology tables", "Non-bidirectional link detection" and "Organization of networks".

  If the preliminary designation of the clearly best CCo candidate in block 52 ultimately results in only a single candidate identity, control proceeds to block 58 and, if needed, the entire desired network In organization, the current CCo is selected in preparation for the operation of the following step (block 60). In operation of block 52, there is a bond between two candidate nodes, for example CCo. If the network being assembled is a distributed network, the activity proceeds to block 54, which implements a specific selection protocol that will be described shortly and performs a single CCo selection. On the other hand, if such a connection exists at the time of setup where the centralized network is being organized, the activity proceeds from block 52 to block 56, again to perform a single CCo selection, as described immediately below. Specific steps are taken.

  Based on what kind of network is being organized, the details of such a selection process are given below under their respective appropriate headings for each of the two different types of ad hoc networks.

CCo Selection—Distributed Network Once the topology map is analyzed, the entire network is organized, and the set N is determined from the topology table, each node selects the node in N most suitable to play the role of CCo. Must be decided. The criteria for selecting the CCo may be different. Any one or a combination of these criteria can be used in selecting the CCo. All the nodes participating in the process must agree and know about the criteria as described in the numbered paragraphs below.

  1. Maximum coverage: Nodes in network N that support bi-directional links with the maximum number of nodes provide the best coverage and can be considered suitable to become CCo. This definition is as follows.

  2. Maximum capacity: As part of the process by which a node creates a topology map, nodes can exchange information regarding the quality of reception of each discovered node. This requires a common agreement among all nodes regarding parameters defining the transmission of inter-node messages, such as transmission power level, modulation depth, coding, etc. This quality indicator communicates the quality of the link or communication channel between the two nodes to the transmitting node and further helps the transmitter determine the best throughput (bits / second) or link capacity possible on a given link. For channels that can be time variable (on a fast time scale), the quality indicator may be less relevant to determine the potential capacity of the link.

  Assuming that the above method or another method not specified herein can be used to determine the link capacity, as the maximum of the minimum throughput of all links to or from the node, or A node that can support the best overall throughput, defined as either the sum of the throughputs of all links, can be selected as the CCo. This node is selected from set N.

  3. Device class: Based on the class of each of the nodes in N, the node in N with the best capability or maximum class can be selected as the CCo.

  4). Minimum duty cycle: In some networks, devices can only send and receive at a given time. In such a system, it is effective to select a node that is not transmitting data for its own purpose (for example, a video server that is transmitting SDTV / HDTV) as CCo. This allows the node to devote most of the processing resources to the network control function and more efficiently use the available channel bandwidth. As part of the topology map formation process, devices can exchange parameters to indicate how likely a node is to communicate. The communication signal can have an additional parameter that can refer to an activity indicator that is the percentage of time that the associated node can spend transmitting and receiving data for purposes other than network control. A node with the lowest activity indicator can be selected as the CCo, along with other suitable criteria such as coverage.

  5. Combination of the above factors: A combination of the above criteria can be used to determine CCo. For example, a higher class device may have a higher priority than a lower class device even though the number of nodes reached by the lower class device is slightly higher. Otherwise, a device that is not sending or receiving data may have a higher priority than a higher class device, but a higher priority for devices that are likely to be transmitting their data. Can not have.

  6). Join Breaker (Block 54): If there is a join between nodes in N to select CCo, the candidate node uses an appropriate contention access protocol to determine which node will become CCo. Any candidate node must listen to the communication channel during a random time interval before sending a signal that can be referred to as a CCo confirmation message for the other nodes. The node that transmits first is CCo by default. All candidate nodes remain silent when they receive such a confirmation message.

  7). Order for selecting CCo: Another way to prevent the use of the combined breaker option can be expressed as: In order to select a CCo, a random selection of a new CCo can be made if there is a connection between nodes in N. FIG. 4 shows this order of selection considerations.

CCo Selection-Centralized Network After basic network organization, with the set N determined from the topology table, each node must determine the most suitable node in N to play the role of CCo. Don't be. The criteria for selecting CCo may be different. Any one or combination of these criteria can be used in selecting the CCo. These criteria must be agreed and known by all nodes participating in the process.

  1. Maximum coverage: Nodes in network N that support bi-directional links with the maximum number of nodes provide the best coverage and can be considered suitable to become CCo. This definition is as follows.

  2. Maximum capacity: Nodes can exchange information regarding the reception quality of each node discovered during the creation of the topology table. To do this requires a common agreement among all nodes regarding parameters that define the transmission of messages in these states, such as transmission power level, modulation depth, coding, etc. This quality indicator communicates the quality of the link or communication channel between the two nodes to the transmitting node and further helps the transmitter determine the best throughput (bits / second) or link capacity possible on a given link. For channels that can be time variable (on a fast time scale), the quality indicator may be less relevant to determine the potential capacity of the link.

  Assuming the above method is used to determine the link capacity, either as the maximum of the minimum throughput of all links to the node or the sum of the throughput of all links to the node A node that can support the best overall throughput defined as can be selected as the CCo. This node is selected from set N.

  3. Device class: Based on the class of each of the nodes in N, the node in N with the best capability or maximum class can be selected as the CCo. Some nodes in the network may not function as CCo. The CCo must maintain device class or device capability information obtained at the time of association. This data must allow the CCo to determine whether the device can or cannot function as a CCo role.

  4). Minimum duty cycle: In an ad hoc network, some devices can only transmit and receive at a given time (half-duplex operation). In such a system, it is effective to select a node that is not transmitting data for its own purpose (for example, a video server that is transmitting SDTV / HDTV) as CCo. This allows the node to devote most of the processing resources to the network control function and more efficiently use the available channel bandwidth. As part of the topology map formation process, devices can exchange parameters to indicate how likely a node is to communicate. The communication signal can create an additional parameter that can refer to an activity indicator that is the percentage of time that a device can spend transmitting and receiving data for purposes other than network control. A node with the lowest activity indicator can be selected as the CCo, along with other suitable criteria such as coverage.

  5. Combination of the above factors: A combination of the above criteria can be used to determine CCo. For example, a higher class device may have a higher priority than a lower class device even though the number of nodes reached by the lower class device is slightly higher. Otherwise, a device that is not sending or receiving data may have a higher priority than a higher class device, but a higher priority for devices that are likely to be transmitting their data. Can not have.

  6). Order for selecting CCo: Since there are many criteria by which CCo can be specified, the next priority order is proposed. If there is a connection between nodes in N to select CCo, the current CCo can randomly select one of the candidate nodes as a new CCo. The order of this selection study is shown in FIG.

  In either of the two selection processes described above, when selecting CCo based on very few criteria, an excellent selection method is to use a combination of “maximum coverage”, “minimum duty cycle” and the above criteria. It is.

  In the foregoing, a new and effective method for selecting the best selected CCo in a distributed or centralized ad hoc network has been described. Such selections can be evaluated and “recommended” using data in the map derived from a complete network topology map.

  Although the preferred embodiments of the present invention have been described above, various modifications and changes can be made within the scope of the present invention.

1 is a block schematic diagram illustrating a network environment selected to illustrate how the present invention is implemented. Fig. 2 is a flow chart illustrating a method of implementing the present invention in connection with both distributed and centralized networks. FIG. 6 is a table showing a representative portion of a complete network topology map (or table) used to implement the present invention for selecting a central coordinator node according to the method of implementation of the present invention. FIG. 6 is a table showing the order of priority of criteria considerations that can be used during the organization of a network in which there is a connection between candidates likely to be CCo.

Explanation of symbols

20, 22, 24, 26, 28 ... nodes, 30, 32 ... network topology, 34, 36, 38, 40, 42, 44 ... interconnects.

Claims (9)

A method that can be used in the task of selecting a central coordinator node while organizing an ad hoc network from a collection of multiple nodes, with each identity, capability and the number and quality of communication links between the associated nodes all In such a way that the organization of the topology map described for a node is such that it is organized at the time of configuration where it is available to all nodes in the set.
Effectively relating all of the nodes to activities leading to the analysis of the topology map;
Effectively performing an all-node participation process to pre-designate the best candidate to be the central coordinator node selected at least thereafter from the results of the association and the results of the analysis. A method that can be used in the task of selecting a central coordinator node.   The implementation of a predetermined reset central coordinator selection criterion derived from a list comprising (a) maximum coverage, (b) maximum capacity, (c) device class / device capacity, and (d) minimum duty cycle. The method of claim 1, wherein the method involves applying at least one of them.   The method of claim 1, wherein the implementation involves applying a preset central coordinator selection criteria focused on selecting a current node characterized by a maximum coverage and a minimum duty cycle.   The association and enforcement step is a predetermined preset center derived from a list including (a) maximum coverage, (b) maximum capacity, (c) device class / device capacity, and (d) minimum duty cycle. The method of claim 1 involved in applying coordinator selection criteria.   (A) The network to be organized is based on the assumption that there is always a central coordinator node, (b) there is actually a current central coordinator node at the time of the implementation, and (c) the result of the implementation The method of claim 4, wherein a join between a plurality of pre-designated best candidates is resolved by a current central coordinator node.   (A) the network to be organized is based on the assumption that there is no central coordinator node at all times, (b) there is actually no current central coordinator node at the time of implementation, and (c) the result of the implementation 5. The resulting combination between a plurality of pre-designated best candidates is resolved by the first node of the combined best candidate in the set to generate a self-confirmation signal as being the central coordinator node. the method of.   The application of the criteria is performed in a preferred sequence having a hierarchical descending order of (1) device class, device capability, (2) maximum coverage, (3) maximum capacity, and (4) minimum duty cycle. 4. The method according to 4. A method that can be used in the task of selecting a central coordinator node while organizing an ad hoc network from a collection of multiple nodes, with each identity, capability and the number and quality of communication links between the associated nodes all This organization is done at the time of configuration where a topology map based on an individual, locally owned, per-node map that describes the nodes is available to all nodes in the set. In the way
For each node, individually relating all of the nodes to the analysis of locally owned topology maps;
Effectively performing an all-node participation process to pre-designate the best candidate to be the central coordinator node selected at least thereafter from the results of the association and the results of the analysis. A method that can be used in the task of selecting a central coordinator node. A method that can be used in the task of selecting a central coordinator node while organizing an ad hoc network from a collection of multiple nodes, including the identity of each node, the capabilities and the number of communication links between the associated nodes and In such a way that the organization of the topology map that describes all nodes from the discovered list of existing nodes is configured when available to all nodes in the population. ,
Associating at least one of all nodes in the analysis of the topology map;
From the result of the association and the result of its analysis, the process is performed by at least one node instead of all nodes in order to pre-designate the best candidate that will at least subsequently become the all-node selection central coordinator node A method that can be used in the task of selecting a central coordinator node with steps.

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